A frame rate can be improved by newly interpolating a frame between consecutive frames of a motion picture. A frame to be interpolated is referred to hereinafter as an interpolation frame.
FIG. 15 is an explanatory view showing an interpolation frame that is generated in general interpolation frame generation processing. Frames 100 and 101 shown in FIG. 15 are two consecutive frames, and an interpolation frame 106 is generated as a frame to be interpolated between them. In FIG. 15, pixels of the given two frames 100 and 101 are indicated by black, and pixels of the interpolation frame 106 whose pixel values are to be specified are indicated by oblique lines.
Each frame includes pixels arranged in the x-axis direction and the y-axis direction. The t-axis shown in FIG. 15 represents time when frames are switched. Although the y-axis of frames is omitted in FIG. 15, FIG. 16 shows the two consecutive frames 100 and 101 and the interpolation frame which are illustrated without omitting the y-axis. Further, of the two consecutive frames, the frame to be displayed precedently is referred to as a first frame, and the frame to be displayed subsequently is referred to as a second frame. In other words, of the two consecutive frames, the precedent frame on the time axis is the first frame, and the subsequent frame is the second frame.
In the case of generating the interpolation frame 106 between the first frame 100 and the second frame 101, the correspondence between a pixel in the first frame 100 and a pixel in the second frame 101 is estimated, and a motion vector from a pixel in the first frame 100 to a corresponding pixel in the second frame 101 is estimated. In FIG. 15, such a motion vector is indicated by an arrow. A motion vector from a pixel at coordinates (xT, yT) in the first frame 100 to a corresponding pixel in the second frame 101 is referred to as (uT, vT).
After estimating the motion vector, a position in which the motion vector from the pixel in the first frame 100 to the corresponding pixel in the second frame 101 passes through the interpolation frame is identified. The position is (xT+uT/2, yT+vT/2). Then, the pixel value of a pixel in the position is set to the average value of the pixel in the first frame 100 and the corresponding pixel in the second frame 101.
For example, in FIG. 15, a pixel 102 in the first frame 100 and a pixel 104 in the second frame correspond to each other. In this case, if the coordinates of the pixel 102 is (xT, yT), and a motion vector 103 from the pixel 102 to the corresponding pixel 104 is (uT, vT), the position on the interpolation frame which the motion vector 103 passes through is (xT+uT/2, yT+vT/2). Then, the pixel value of (xT+uT/2, yT+vT/2) in the interpolation frame (i.e. the pixel value of a pixel 105 in FIG. 15) is defined as the average value of the pixel values of the pixels 102 and 104.
Further, in the estimation of a motion vector, template matching is performed in units of blocks of a certain size. For example, there is a technique that identifies a motion vector by searching, with respect to each pixel of the first frame 100, for a block in the second frame 200 corresponding to a block of a certain size centering on the pixel. An example of the template matching is described in the patent document 1. In the patent document 1, a motion vector detection method is described that calculates the sum of absolute differences of the respective pixels of a reference block of an image of a previous field and a reference block of an image of a subsequent field with respect to each candidate for a motion vector and sets a vector indicating the minimum value as a motion vector. Further, in the patent document 2, a motion detection method is described that calculates a motion vector from a plurality of candidate vectors.
In the template matching, it is presumed that the shape of an object to be displayed is a block of a certain size, and a pair of blocks of the certain size corresponding to each other is identified between two consecutive frames.
[Patent Document 1]
    Japanese Unexamined Patent Application Publication No. 2006-166061 (Paragraph 0011)[Patent Document 2]    Japanese Unexamined Patent Application Publication No. 2005-318576 (Paragraphs 0031-0033)